1. Field of the Invention
The present invention relates to a motor controller capable of suppressing resonant vibration (in this specification, vibration resulting from resonance phenomenon will be referred to as resonant vibration) occurring in a motor at a specific rotation speed.
2. Description of the Related Art
In order to cool down a computer, a cooling fan that takes in the ambient air into a casing is attached to the casing that accommodates the computer such as a CPU.
As an example of cooling fans, JP 5-95063 A discloses a variable speed cooling fan that changes a rotation speed according to the temperature of the casing.
However, in the variable speed cooling fan, a switching frequency of current supplied to a motor coil and a mechanical resonance frequency of the motor influence each other in a specific rotation speed region. As a result, the motor itself oscillates and vibration occurs, which may increase the noise of the cooling fan.